Measuring permeability by the thermal expansion method for rigid or highly permeable gels

George W. Scherer

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21 Scopus citations


The permeability (D) of a gel can be determined by analysis of its thermal expansion kinetics: as the gel is heated, the expanding liquid stretches the solid network like a spring; during an isothermal hold, the liquid drains out and the gel returns to its initial dimensions at a rate that depends on D and the elastic modulus of the network. However, if the network is too rigid or D is too high, the dilatation of the network may be too small to measure easily. The measured expansion increases with the viscosity of the pore liquid, so D is easier to measure after the gel is rinsed in a higher alcohol. For example, a thermally aged silica gel that shows no measurable expansion in ethanol exhibits a large thermal strain after the pore liquid is changed to 1-octanol. It is important to demonstrate that the same permeability is obtained regardless of the liquid employed (i.e., that flow in the small pores of the gel does not give rise to liquid-specific effects), so we examine the thermal expansion of a silica gel rinsed successively in ethanol, 1-octanol, and 1-decanol; the gel is compliant enough so that D is measurable in all these liquids. The permeability is found to be the same, but the expansion is much more easily measured for the more viscous alcohols.

Original languageEnglish (US)
Pages (from-to)31-40
Number of pages10
JournalJournal of Sol-Gel Science and Technology
Issue number1
StatePublished - Jan 1994

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • General Chemistry
  • Biomaterials
  • Condensed Matter Physics
  • Materials Chemistry


  • decanol
  • octanol
  • permeability
  • thermal expansion


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